Moistureproof material



Patented Nov. 26, 1929 UNITED STATES;

PArENr o ric E WILLIAM HALE CHARGE AND KARL EDWIN PRINDLE, OF BUFFALO,NEW YORK, ASSIG-NORS, BY MESNE ASSIGNMENTS, 'IO DU PONT CELLOZPHANECOMPANY, INC., OF NEW YORK, N. Y., A CORPORATION OF DELAWAREMOISTUREPROOF MATERIAL 11' 0 Drawing.

It is the object of our invention to provide a materialwhich may be madeeither in the form of thin sheets or films and which shall be not onlywaterproof in the ordinary sense but moistureproof.

It is a further object of our invention to provide a material having theabove characteristics and which shall also be very thin, transparent,flexible, colorless, odorless and non-tacky. Waxed paper is waterproofin the ordinary sense of the word and also moisturcproof in Varyingdegrees, but is not transparent and, moreover, is quite thick and stiif,cracking when it becomes crumpled. The products of our invention is somefive to ten times thinner than waxed paper and is at least asmoistureproof, and because of these qualities and the other qualitiesnoted above, the

uses which may be made thereof are much reater than those for whichordinary waxed paper can be used.

In carrying out our invention we employ a composition comprising a base,a gum or a resin, a wax or wax-like material, and a plasticizer. Thesematerials maybe mixed in different proportions, depending upon thequalities required of the finished composition.

For the base We prefer to use a cellulosic derivative, such as acellulose ester or ether, and more particularly a nitrocellulose of thepyroxylin type, because of its economy, although cellulose acetate, orethyl or methyl cellulose may be employed with satisfactory results. Thebase is preferably one yielding a solution of low viscosity, becausethis quality permits working with more highly concentrated solutionsthan could be used with a base yielding a solution of high viscosity.

For the gum we have found that gum dammar is very satisfa-ctory,'eithersingly or in combination with certain other gums. Some of the other gumsthat are preferably used either singly or in combination are ester'gum,rosin, gum mastic, or the copal resins. It is to be understood that thegums may be either natural or synthetic, as it is possible-tomanufacture certain synthetic gums that are fairly satisfactorysubstitutes for the natural ones.

' For the wax we prefer to use a high melt- Applicat ion filed January3, 1927. Serial No. 158,816.

to moisture than the low melting paraffin. The paraffin being colorlessand odorless is preferable to other waxes from these standpomts and alsofrom the standpoint of economy. Examples'of other waxes which may beused are ceresin wax, either hard or soft,

and beeswax. The above Waxes may be used either singly or mixed witheach other or with other Waxes as may be found desirable.

For the plasticizer we preferably employ one of the compounds ormixtures of compounds having a high boiling point, and which are knownas plasticizers or softenors for cellulose esters or others such asnitro cellulose, cellulose acetate, ethyl cellulose, etc. We prefer touse a plasticizer which shall be substantially odorless and haveobtained satisfactory results from using tricresyl phosphate, tri-phenylphosphate, di-

amyl phthalate or di-butyl phthalate, or

a Per cent Base 30 to 70 Gum... 30 to 60 Wax 2 to 6 Plasticizer 5 to 30The exact proportions of the various ingredients will vary according tothe qualities desired in the finished product, and these qualities'willdepend upon the use to which the.

product is to be put. For example, if freedom from tackiness is notessential, then the pro portions and kinds of gum and wax may be variedtoobtain a mixture which will be easier to make and yet Will have allthe desired qualities except freedom from tackiness. By

50 ing paraflin wax as giving greater resistance varying the proportionsof the ingredients it is possible to obtain acomposition with widevariations in the various qualities. By vary ing the quality of wax wecan obtain a wide range in the degree of resistance to moisture; byvarying the quantity of, or even omitting entirely, the plasticizer,all'degrees of flexibility may be obtained; and by regulating the 1nature. and quantity of the gum, wax and plasticizer, a wide range inthe degree of transparency may be obtained.

The amount of base, which is preferably a nitrocellulose of thepyroxylin type, is usually chosen with respect to the particular gumwhich is employed. The ratio by weight of gum to base may vary betweenthe limits 2: I

and 1: 2. \Vhen the ratio exceeds 2: 1 cracking of the material results.\Ve have found that the best ratios are within the limits of 1:1and1:1%.

The quantity of gum used depends upon the gum which is chosen,particularly with respect to its complete solubility and its ability toblend with the wax. aud also the amount of base used with it. Thepreferred ratio of gum to base has been given above. A high ratio of gumto base renders the material brittle when used as a coating and preventsproper adhesion of the coating to the material to which it is applied. Atoo low per cent-age of gum will result in a poor blending with the waxand thus a decrease of transparency and an increase in greasiness ortackiness.

The wax preferably should be kept below 10% by weight of the totalsolids, and the best results are obtained when this percent: age is keptbetween 2% and 6%. When the percentage approaches or exceeds 10%,crystallization of the waxes begins, thus decreasing transparency.However, the moistureproof quality is not materially affected providingthe same ratio of plasticizer to wax is retained and, therefore, arelatively large percentage of wax may be used when a relatively lowdegree of transparency is permissible.

The amount of plasticizer depends chiefly on the amount of wax and alsoupon the ratio by weight of the amount of gum to the amountof base.lVhen this ratio is relatively large, a greater quantity of plasticizershould be used to overcome the brittleness which is developed by the.relatively large amount of gum. Moreover, the degree ofmoistureproofness depends partly upon theratio of the wax to theplasticizer and, therefore, this ratio partly determines the percentageof plasticizer employed. The ratio of plasticizer to wax may varybetween the limits of 1:1 and 4:1 with good results in the way ofachieving a moistureproof material, but for most purposes we have foundthat the best ratio is between the limits of 2 :1 and 3:1.

lVc have discussed above the proper ratios of gum to base and ofplasticizer to wax. It now remains to discuss the preferred ratio of thecombined weights of base and gum to the combined weightsof wax andplasticizer. The combined weights of base and :gum are usually severaltimes greater than. the combined weights of wax and plasticizer. Theratio of the weights ofb'ase and gum combined to the weights of wax andplasticizer combined may vary between the limits of about2.3:l and 10:1,but we find that the preferred ratio is between 4:1 and 8:1. If theratio is less than 2.3:1 the. sheet or coating will either become tackydue to the high percentage of plasticizer or will become opaque andgreasy due'to the high percentage of wax. \Vhen the ratio of weights ofgum and base .to plasticizer and wax is greater than 10:1 the sheet orcoating will usually have a tendency to crack due to the small amount ofplasticizer and the relatively large amount of gum, or will possess anundesirably low degree of moisture resistance due to the low amount ofwax employed.

It is seen from the above that, in determining the ingredients, thenature and quantity of any one must be chosen with respect to that ofall the other ingredients if we are to obtain a product which willexhibit at once all of the desirable properties already enumerated. Inthis matter the choice is defined by the above approximate limits, butthe following examples illustrate several excellent combinations whichhave been employed with success. We have classed as solids theingredients of the composition which are dissolved in a solvent for thepurpose of manufacturing the finished article. While the plasticizer mayappear as a liquid, nevertheless, it is non-volatile and remains in thecoating after it is dry, and therefore, for the purpose of thisapplication and for convenience, all of the ingredients are referred toas solids.

Solid constituent luxample 1:

Per cent ha sed on total weight of solids Nitrocellulose 52 Ester gum 35Di-butyl phthalate 8.7- Paraflin 4.3 Example 2:

Nitrocellulose 50 Gum dammar 34 Tri-cresyl phosphate 12 Paraffin 4method of application and to the nature andv percentages of the solidingredients. The solvent mixture must be such as to retain all of thesolid ingredients in a homogeneous solution until all solvents areevaporated. The wax and base ordinarily do not mix to form a clear filmbut by a proper choice of equality and kind of gum it has been foundpossible to make the combined gum and wax mix with the base andplasticizer. The solvent mixture must then be chosen to retain the gum,wax,

- of the coating which would cause cooling of the surrounding atmosphereand precipitation of water vapor on the material. The

coating or sheet is then dried preferably with warm air not exceeding 90or 100 C. It

. is preferable to keep the temperature of the air above the meltingpoint of the wax or waxes used, thereby preventing separation orcrystallization of the wax during the drying operation. It is alsopreferable to use air low in moisture content to aid in evaporation ofthe solvents. By this means it is possible to effect a very great savingin time of drying.

' After drying the product is preferably subjected to the action of heatand preferably steam for a short time in order to more thoroughly removethe last traces of solvents and thus make the product entirely odorless.

While the particular solvent must be determined separately for theparticular composition, we give below the specific solvent combinationsWhichwe have found may be used with the respective examples ofcompositions given above.

Per cent based on total volume of solvent Solvent for Example 1:

Alcohol 25 Ether 43 Toluene 18 Butyl acetate 14 Solvent for Example 2:

Ethyl acetate 62 Toluene 27 Alcohol 9 Butyl acetate 2 The solution maybe used in a variety of ways. It may be cast by known methods into thinsheets which are transparent, flexible, have the required tensilestrength and at the same time are several times'more moistureproof thananything hitherto known and that havethe other qualities mentionedabove. These sheets may be made of any desirable thickness, a thicknessof .0003" to .001 being suflicient when the sheets are to be applied tosheets or films of regenerated cellulose.

Again the solution may be applied in the form of a coating to sheets orfilms of cellulose regenerated from viscose, the coating beingdone bysuitable machines. Sheets of regenerated cellulose have been employed aswrappin'gs for various substances which it is desired to protect fromdust, handling by the buying public, fly specks, etc. Though they arethin, transparent and flexible they are poorly resistant to the passageof moisture. It has been found that sheets of regenerated cellulosecoated on one or both sides with the compositions above-described, thecoatings being .00005 to .0005 thick or thicker, when submitted tostandard tests give values which clearly indicate that said sheets areat least from one hundred to two hundred times more moistureproof thanthe uncoated sheet and at least two or three times as lnoistureproof aswaxed paper. Moreover, this result is achieved without sacrificing anyof the very desirable qual ities of transparency and flexibility whichare possessed by the sheets of regenerated cellulose. It is well-knownthat a waxed paper is stiff and relatively thick as well as opaque,whereas a sheet of material constructed according to our-invention or asheet of regenerated cellulose coated with our composition isvery thin,flexible and transparent as well as highly moistureproof. In practice ithas been found suflieient to apply about .00010 to each side of a sheetof regenerated cellulose which usually has a thickness of .0007" to.002". Coating on one side is sufficient but we prefer to coat bothsides. The resulting sheet is still very thin and the necessarytransparency and flexibility is retained.

The above is merely given as an illustration of one use to which ourinvention may be applied. If desired'to make a thicker .sheet ofmeterial, regenerated cellulose sheets may be built up to form alaminated sheet which may then be coated and which will I still maintainthe desired characteristics, the

flexibility obviously decreasing as the thickness increases. Increasedthickness of the coating will obviously increase the resistance tomoisture and, therefore, the thickness employed will depend largely uponthe use to which the finished article is to be put. For instance,regenerated cellulose sheets may be built up into a laminated structureforuse in automobile curtains and when so used the eoating applied formoistureproof purposes will naturally be thicker than that applied to asingle sheet that is to be used for wrapping a cake or other articles offood.

A sheet of coated regenerated cellulose used for the purpose of wrappingan article therein will obviously not only keep the moisture in thepackage but will prevent the entrance of moisture, thereby preservingthe contents, such as food, at the proper and desiredmoistness. At thesame time if the package is subjected to moisture from without thecontents are protected.

One common fault of many waterproof coatings utilizing wax is the factthat their surfaces are or become greasy. This fault is caused by thepresence of wax in the coatinguncombined with the other ingredients. \Vehave succeeded in using wax and thereby making the product waterproofand moistureproof, but at the same time have avoided making it greasy?The product made according to our invention is one which has all of thedesired propcrties of 1noistm'eproofness, flexibility, tensile strength,transparency, non-tackincss, color and lack of odor.

By the term moistureproof used herein, we mean the ability to resist thediffusion of water vapor to an extent at least as great as or exceedingthat displayed by ordinary waxed papers employed as wrappers andfunctioning to resist the penetration of water vapor therethrough to asubstantial degree for a substantial period of time depending on thearticle being wrapper and/or being approximately 7 times or more aseffective as uncoated sheets or films of regenerated cellulose whentested under the same conditions.

We claim 1. An article of manufacture comprising a sheet or film ofregenerated cellulose combined with a moistureproofing composrtlon. 2.An article of manufacture comprising a sheet or -film of regeneratedcellulose combined with a moisture-proofing composition, said articlebeing transparent, flexible, and non-tacky.

3. An article of manufacture comprising a sheet or film of regeneratedcellulose combined with a moisture-proof, transparent, and non-tackyfilm.

4. A wrap-ping material comprising a sheet 7 or film of regeneratedcellulose combined with a moistureproofing composition.

5. A wrapping material comprising a sheet or film of regeneratedcellulose combined with a moistureproofing composition, said articlebeing transparent, flexible and non-tacky. I

6. A wrapping material comprising a sheet or film of regeneratedcellulose combined with a. moistureproof, trans-parent, flexible andnon-tacky film.

7. An article of manufacture comprising a sheet or film of regeneratedcellulose having a coating comprising a cellulose derivative, a wax anda gum, said article being moistureproof, transparent and non-tacky.

8. An article of manufacture comprising a sheet-0r film of regeneratedcellulose having a coating comprising a cellulose derivative, a wax, aplasticizer and a gum, said article being moistureproof, transparent,flexible and non-tacky.

9. An article of manufacture comprising a sheet or film of regeneratedcellulose having a coating comprising a cellulose derivative, a wax, aplasticizer and a gum, said article 'being moistureproof, transparent,flexible and non-tacky, the ratio of the gum to the cellulose derivativebeing between the limits of 2: 1 and 1:2 by weight.

10. An article of manufacture comprising a sheet or film of regeneratedcellulose having a coating comprising a cellulose derivative, a wax, aplasticizer and a gum, said article being moistureproof, transparent,flexible and non-tacky, the ratio of plasticizer to wax being betweenthe limits of 1 :1 and 4: 1 by weight.

11. An article of manufacture comprising a sheet or film of regeneratedcellulose having a coating comprising a cellulose derivative, a wax, aplasticizer and a gum, said article being moistureproof, transparent,flexible and non-tacky, the ratio of thecombined weights of gum andcellulose derivative to the combined weights of wax and plasticizerbeing between the limits of 2.3 :.1 and 10: 1.

12. An article of manufacture comprising a sheet or film of regeneratedcellulose" having. a coating comprising a cellulose derivative, a wax, aplasticizer and a gum, said article being moistureproof, transparent,flexible and non-tacky, the ratio of the gum to the cellulose derivativebeing between the limits of 2:1 and 1:2 by weight and the ratio ofplasticizer to wax being between the limits of 1: 1 and 4: 1 by weight.g

13. An article of manufacture comprising a sheet or film of regeneratedcellulose having a coating comprising 30%70% of a cellulose derivative,30%60% of a gum, less than 10% of a wax and 5%30% of a plasticizer,

said article being moistureproof, transparent,

flexible and non-tacky.

14. An article of manufacture comprising a sheet or film of regeneratedcellulose having a coating comprising nitrocellulose, gum dammar,tri-cresyl phosphate and parafiin,

said article being n'ioistureproof, transparent,

flexible and non-tacky. I

15. An article of manufacture comprising a sheet or film of regeneratedcellulose having a coating comprising 50% nitrocellulose, 341% gumdammar, 12% tri-cresyl phosphate and 4% .paraflin, said article beingmoistureproof,-transparent, flexible and non-tacky.

16. A wrapping material comprising a sheet of regenerated cellulosecombined with a moistureproof, transparent, flexible, and non-tacky filmand being approximatel at least 7 times as eil'ective as the uncoated seet of regenerated cellulose, said film having a thickness ofapproximately 1.6 ten-thousandth of an inch.

17. An article of manufacture comprising a sheet or film of regeneratedcellulose having CERTIFICATE OF CORRECTION.

Patent No. 1,737,187.

Granted November 26, 1929, to

word "quality" read "quantity"; page 3, line (Seal) WILLIAM HALE CHARCHET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,line 3, for t the 7i, strike out the word "that;

same page, line )5, for the word "or" read "to", and line 118, for thenuisspelled word "meterial" read "material"; page 4, line 36, for theword wrapper" read "wrapped"; and that the said Letters Patent should beread with these corrections therein that the same may conform to therecord of the casein the Patent Office. v

Signed and sealed this 31st day of December, A. D. 1929.

M. J. Moore, Acting Commissioner of Patents.

